1. Field of the Invention
The present invention relates, in general, to a coupling assembly between two pipes and, more particularly, to a coupling assembly for providing a connection between a lined pipe and an unlined pipe.
2. Description of Related Art
Typical oilfield pipes are produced from steel and corrosion resistant alloys or materials. During production, injection, and disposal well operations, the pipes are exposed to hydrocarbon fluids and gases which contain brine water, hydrogen sulfide, carbon dioxide and other corrosive compounds. The combinations of fluids and gases transmitted by oilfield pipes under extreme temperatures and pressures create a variety of acidic, caustic and corrosive conditions that attack and corrode tubular goods. One solution to prevent corrosion of oilfield steel pipes is to coat the inside of the pipes with a plastic layer or other corrosion resistant coating.
An alternative to prevent corrosion of oilfield pipes is to insert a corrosion resistant liner into the steel pipe. Such liners may be made of polyvinyl chloride (PVC), polyethylene (PE), glass fiber reinforced epoxy resin (GRE), or other reinforced polymer resins. Typically, these liners are up to 45 feet long and have an outside diameter sized to tightly fit within the inside diameter of the steel pipes or to loosely fit creating an annulus, which is subsequently grouted.
In many instances, lined pipes are used in the same pipe line as unlined pipes. The unlined pipes and couplings are usually manufactured from corrosion resistant materials. Accordingly, appropriate threaded coupling assemblies are required to connect the unlined pipe with lined pipe in an end-to-end relationship. Coupling assemblies are also required to connect the internal liner that provides protection for the lined pipe and pipe threaded connection area against internal corrosion and ensures that the internal liner remains secured.
There are a large number of pipe end constructions and thread constructions employed by various pipe manufacturers to assure against fluid and gas leakage. Due to the presence of unique metal-to-metal torque shoulders and metal-to-metal seal areas, many of these pipe ends and thread constructions known in the art require a custom built liner or coupling assembly unique to the pipe end and potentially even a custom pipe end thread design to accommodate an internal lining system.
One method known in the art utilizes an internal lining system that requires the insertion of a somewhat flexible plastic tube inside steel tubing and filling the annular space between the plastic tube and steel tubing with mortar. The inner plastic tube, or liner, is capped or terminated at the end of the pipe with a flange, known as a “flare”. The flare ends provide a surface area for compression of a barrier ring, such as an elastomeric barrier ring, in the coupling assembly.
Additionally, lined pipes are often coupled to an unlined box of an accessory such as a valve. Accordingly, a need exists for a pipe coupling that provides a smooth transition between a lined pipe and an unlined pipe or box accessory.